Uncoated razor blades, despite their sharpness, cannot be employed for shaving a dry beard without excessive discomfort and pain, and it is as a practical matter necessary to employ with them a beard-softening agent such as water and/or a shaving cream or soap. Even with the beard-softening agent, the pain and irritation produced by shaving with uncoated blades are due to the excessive force required to draw the cutting edge of the blade through the beard hairs, the force of which is transmitted to the nerves in the skin adjacent the hair follicles from which the beard hairs extend, and, as is well known, the irritation produced by excessive pulling of these hairs may continue for a considerable period of time after the pulling has ceased. Blade coatings were developed to solve these shortcomings. However, conventional razor blades generally have increasing cutting forces with use due to the outer coating wear and adhesion loss.
Fischbein, U.S. Pat. No. 3,071,856, issued Jan. 8, 1963, describes fluorocarbon-coated blades, particularly polytetrafluoroethylene-coated blades. The blades may be coated by (1) placing the blade edge in close proximity to a supply of the fluorocarbon and subsequently heating the blade, (2) spraying the blade with a fluorocarbon dispersion, (3) dipping the blade into a fluorocarbon dispersion or (4) by use of electrophoresis. The resulting blade was later heated to sinter the polytetrafluoroethylene onto the blade edge.
Fischbein, U.S. Pat. No. 3,518,110, issued Jun. 30, 1970, discloses an improved solid fluorocarbon telomer for use in coating safety razor blades. The fluorocarbon polymer melts between 310° C. and 332° C. and at 350° C. has a melt flow from 0.005 to about 600 grams per ten minutes. The preferred polymers are believed to have molecular weights ranging from about 25,000 to about 500,000 grams/mole. For best results, the solid fluorocarbon polymer is broken down into particles ranging from 0.1 to 1 micron. The dispersion is electrostatically sprayed onto stainless steel blades.
Fish et al, U.S. Pat. No. 3,658,742, issued Apr. 25, 1972, discloses an aqueous polytetrafluoroethylene (PTFE) dispersion containing Triton X-100 brand wetting agent which is electrostatically sprayed on blade edges. The aqueous dispersion is prepared by exchanging the Freon solvent in Vydax brand PTFE dispersion (PTFE+Freon solvent), distributed by E.I. DuPont, Wilmington, Del., with isopropyl alcohol and then exchanging the isopropyl alcohol with water.
Trankiem, U.S. Pat. No. 5,263,256, issued Nov. 23, 1993 discloses an improved method of forming a polyfluorocarbon coating on a razor blade cutting edge comprising the steps of subjecting a fluorocarbon polymer having a molecular weight of at least about 1,000,000 grams/mole to ionizing radiation to reduce the average molecular weight to from about 700 to about 700,000 grams/mole; dispersing the irradiated fluorocarbon polymer in an aqueous solution; coating said razor blade cutting edge with the dispersion; and heating the coating obtained to melt, partially melt or sinter the fluorocarbon polymer.
Trankiem, U.S. Pat. No. 6,228,428 issued on May 8, 2001 discloses a method of forming a polyfluorocarbon coating on a razor blade cutting edge which comprises subjecting a fluorocarbon polymer having a molecular weight of at least 1,000,000 grams/mole in dry powder form to ionizing irradiation to reduce the molecular weight of the polymer, forming a dispersion of the irradiated polymer in a volatile organic liquid, spraying the dispersion on to a razor blade cutting edge and heating the coating obtained to sinter the polyfluorocarbon. The polyfluorocarbon preferably is polytetrafluoroethylene and irradiation preferably is effected to obtain a telomer having a molecular weight of about 25,000 grams/mole.
Kwiecien et al., U.S. Pat. No. 5,985,459, issued Nov. 16, 1999, describes a process for treating polyfluorocarbon coated razor blade cutting edges with a solvent which produces a blade edge which exhibits lower initial cutting forces which correlates with a more comfortable first shave over conventional razor blade cutting edges which exhibited high initial cutting forces.
Polytetrafluoroethylene coatings on razor blade cutting edges are clearly known in the art. Furthermore, it appears that various solvents systems have been proposed in the literature for polytetrafluoroethylene.
However, the art fails to appreciate the importance of a thin PTFE coating which is maintained during the initial or first shave but also for the majority of later shaves. Furthermore, the art is silent on selective removal of polytetrafluoroethylene from razor blade cutting edges, followed by additional coating with polytetrafluoroethylene.
It is an object of the present invention to provide a razor blade cutting edge with a thin, well adhered coating which provides significantly improved cutting force effects which are also sustained with use when compared with the prior art. This improvement in cutting force translates to an improved first shave and improved subsequent shaves.
It is also an object of the present invention to provide a razor blade which causes fewer nicks, improves comfort, and/or improves closeness.
Furthermore, it is an object of the present invention to provide a method producing these improved blades. The process utilizes novel processing steps.
These and other objects will become evident from the following disclosure.